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Dell Compellent

Dell Compellent

� Mixing RAID types within a pool or disk group set is possible
� Tiering is done at 2 MB by default, though administrators have the option to manage storage blocks at 512 KB or 4 MB pages
� Tiering profiles can be applied to single LUNs or groups of LUNs
� Profiles specify not only the tiers to be used for each volume, but also the disk types, rotational speeds and RAID levels within each tier.
� With Dell Compellent there is no write penalty for migrating data to lower tiers.
Tiered storage solutions within traditional storage architectures cannot deliver the same level of write performance. In those solutions, data is written to a particular block and kept in that block. If the block is migrated to tier 3 and a new write comes in for that volume, the write will occur on tier 3.
� Dell Compellent snapshots do not reside within the volume with production data � they sit outside the production volume in pages within the general virtual storage pool
� Dell Compellent Fast Track augments Automated Tiered Storage by delivering optimal placement of data on each individual disk.
Fast Track uses the intelligence continuously collected by the Dell Compellent system to identify the most active, frequently accessed blocks of data on each spindle. It then places those data blocks together on the outer tracks of each drive. Keeping the head focused on that one area of the disk, where the active data resides, delivers better performance than if the head were forced to move all over the disk.
� Writes are always written to tier 1 RAID 10, large sequential write workloads will hit tier 1,
Migration occurs automatically at a set time defined by the user, or on demand, while the system is
still online. The migration process runs in the background and does not affect data availability or
application performance. There is no need to bring down an application, pause I/O or wait for a
minimum I/O requirement. If a read request comes in to a page that is being moved, the request is
satisfied from the original placement of the page. The page is then moved after the read is complete.
If a write request comes in, it will not interfere with the migration process, as new information is
always written to tier 1, RAID 10�and therefore is not eligible for migration. Overwriting a block of
protected information also occurs on tier 1, RAID 10, so moving a block of data receiving writes simply
will not occur. There is never a situation when application I/O is denied�application requests always
receive priority.
In the Dell Compellent architecture, new data is written by default to tier 1, RAID 10 storage to
provide the best write performance.
� Activating the tiering functionality requires a module-specific license, but perpetual licensing ensures that organizations only incur additional licensing expenses when adding more capacity to an existing system. Upgrading to a new controller with the latest technologies does not require a new software license, as is the case with other solutions.
� In the Dell Compellent architecture, new data is written by default to tier 1, RAID 10 storage to provide the best write performance. Replays move to a lower storage tier with RAID 5 or 6 protection during the next migration cycle within a 24-hour window. And over time, according to the tiering profile, infrequently accessed blocks of data move to a lower storage tier and RAID level, or to a different RAID level within the same tier. Moving this read-only data from RAID 10 to RAID 5 within the same tier enables administrators to maintain the same read performance.
Not sure that that read performance will be the same when a block of data within a tier is moved between RAID types (RAID 5 read perform is superior to RAID 10)
� When new data needs to be written to an existing block that has since been converted to read-only and migrated to a lower tier, those writes are redirected to the tier 1, RAID 10 storage. A new writable block is automatically allocated to provide the highest transaction performance. Virtual pointers utilize the use characteristics of those blocks to maintain data continuity. All data is written to tier 1, yet snaphsots move to the lower tier available within 24 hours for the highest write and read performance possible. Virtual pointer retain continuity between all associated blocks.

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